Antifungal Potential of Nostoc Commune Extract against Saprolegnia Australis

Saprolegnia, a ubiquitous oomycete, is the predominant causative agent of Saprolegniosis, a dermatological infection in
fish, and is accountable for substantial economic losses within the aquaculture industry. The necessity for a novel and
efficient drug against the Saprolegnia species is of significant importance, particularly under the ban on malachite green
oxalate in numerous countries and its inappropriate alternatives, such as formalin. The study encompassed two primary
phases. Firstly, Saprolegnia species were isolated and characterized in water samples using culturing, LCB staining, PCR,
gel electrophoresis, and DNA sequencing. Secondly, the antifungal activity and chemical constituents of Nostoc commune
were assessed via well-diffusion, MIC/MFC assays, and GC-MS. Throughout the characterization methods, Saprolegnia
australis was identified as the mold species present in the water samples. Additionally, the antifungal properties of the
Nostoc commune extract were found to be satisfactory, as evidenced by a 30mm zone of inhibition and an MIC value
of 2.5 mg/ml. In the present study, the saprolegniosis pathogen, Saprolegnia australis, was successfully identified and
isolated from the ponds in the Mazandaran region where Oncorhynchus mykiss was present, thus marking a significant
milestone as the first documented instance of its presence in Iran. Furthermore, the study presented a novel and promising
therapeutic agent with the potential to effectively alleviate and mitigate the occurrence of fish skin infections, thus offering
a new approach to combat this growing concern in aquaculture.